This invention relates generally to optical couplers for fiber-optic systems. More particularly, it provides a novel type of coupling devices that permit fiber-optic components to be aligned in various ways, including an angled-axis alignment.
Fiber-optic networks are emerging as the transmission media of choice of telecommunications. Crucial to the performance of a fiber-optic network is the precise alignment and reliable coupling of various fiber-optic components, such as optical fiber carriers, GRIN lenses, and optical filters.
FIG. 1A depicts a method prevalent in the art for coupling optical fibers to a GRIN lens. By way of example, an optical fiber carrier in the form of a fiber holder 100, carrying two optical fibers 101, 102, and a GRIN lens 103 are brought together in close proximity and held in place by an epoxy joint 104. Both UV epoxy and high temperature epoxy are generally employed as the adhesive agent. In some applications, the assembly may involve a two-step process: a UV epoxy is applied first as a fixing to secure the alignment of two adjacent optical elements, such as fiber holder 100 and GRIN lens 103; and a high temperature epoxy is then added to further strengthen the coupling. Since the UV epoxy is considerably viscous, its application also serves to prevent the high temperature epoxy from spreading over to the sensitive optical surfaces.
The above prior art method of coupling fiber-optic elements renders several shortcomings, notably: 1) a bulky epoxy joint often cracks as ambient temperature fluctuates, due to different thermal expansion properties optical elements and epoxy may possess; and 2) moisture tends to degrade the performance of epoxy. Consequently, the alignment and the coupling between fiber-optic elements deteriorate over time, affecting the overall stability of the optical network. Moreover, because of the aforementioned problems inherent to epoxy, any gap between two fiber-optic elements bridged by epoxy, such as gap 105 between fiber holder 100 and GRIN lens 103 in FIG. 1A, must be small, which dictates that GRIN lens 103 in this case have a precise pitch, typically a quarter-pitch (0.25). This is an expensive, and at times impractical, proposition.
FIG. 1B provides an exaggerated depiction of the spatial arrangement between fiber holder 100 and GRIN lens 103 shown FIG. 1A. GRIN lens 103 is used to collimate and focus light beams 115, 116 emerging from fibers 101, 102 respectively to point 107 on its back-end face 108, so that light can be passed onto succeeding fiber-optic elements in the network. Because light refracts at a front-end face 109 of fiber holder 100 and subsequently at a front-end face 110 of GRIN lens 103, an axis 111 of GRIN lens 103 must be oriented at an angle xcex8, albeit small (typically about a few degrees), relative to an axis 112 of fiber holder 100, to ensure that light beams 115, 116 eventually converge to the designated location, point 107.
FIGS. 2A-2B show two other prior art fiber-optic couplers, disclosed in U.S. Pat. No. 6,023,542. In FIG. 2A, a fiber holder 33, carrying two optical fibers 30, 31, is enclosed in a quartz cylinder 46 on one end and coupled to a GRIN lens 34 by way of an epoxy 48 on the other. Cylinder 46 and GRIN lens 34 are further arranged to center in a cylindrical housing 47. Despite the presence of two cylindrical housings 46, 47 in this case, the coupling between fiber holder 33 and GRIN lens 34 relies nonetheless on epoxy 48, rendering it susceptible to the same shortcomings as described above. In the optical coupler shown in FIG. 2B, a GRIN lens 35 and a fiber holder 36 are bridged and held in place by a quartz cylinder 44, which is further telescoped within a second cylindrical housing 45. The physical arrangement in this system, however, does not permit fiber holder 36 and GRIN lens 35 to be aligned in such a way that their respective axes are oriented at an angle, such as the angled-axis alignment illustrated in FIG. 1B.
Hence, there is a need in the art for more effective, reliable, and versatile fiber-optic couplers that overcome the shortcomings of the prior art coupling devices.
Accordingly, it is a primary object of this invention to present a novel class of fiber-optic couplers that enable fiber-optic elements in an angled-axis alignment to be coupled in a secure and reliable manner. It is another object of the present invention to permit a variable gap between two successive optical elements. It is a further object of the present invention to provide methods for coupling fiber-optic elements.
An important advantage of the fiber-optic couplers of the present invention is that they allow fiber-optic elements to be spatially arranged in various ways, yet still attaining secure and reliable coupling. Another advantage of the fiber-optic couplers of the present invention is that the coupling is less susceptible to extraneous effects such as temperature variations and moisture erosion. Moreover, by allowing a variable gap between two optical elements in a fiber-optic coupler of the present invention, a variety of GRIN lenses with less than a quarter-pitch can be employed, which is highly desirable in practice. Further advantages of the fiber-optic couplers of the present invention include their simple assembly, versatility, and adaptability for a variety of applications.
These and other objects and advantages of the present invention will become apparent from the following description and accompanying drawings.
The present invention provides a fiber-optical coupler in which two or more optical elements are bridged and held in place by a sleeve. A first side of the sleeve partially encompasses and is in contact with a first optical element, and a second side of the sleeve partially encompasses and is in contact with a second optical element via an adhesive agent. The length and the inner diameter of the bridging sleeve can be so chosen to allow the axes of the first and second fiber-optic elements to be oriented at an angle. Such an alignment is termed an angled-axis alignment, hereinafter.
The fiber-optic coupler of the present invention further permits a variable gap of empty space between the first and second optical elements. In an application where the first optical element is a fiber holder and the second optical element is a GRIN lens, for instance, the allowance of a gap permits a GRIN lens with less than a quarter-pitch to be used. In addition, there can be one or more optical elements sandwiched between the first and second optical elements.
By choosing a sleeve having thermal expansion properties and geometrical attributes that closely match those of the optical elements it embraces, the coupling between the optical elements in the fiber-optic coupler of the present invention is much less susceptible to ambient temperature variations and moisture erosion, hence more reliable and enduring.
The bridging sleeve is typically made of glass, or metal (e.g., stainless steel). The inner cross-section (i.e., the cross-section of the hollow interior) of the sleeve may have varying shape and size along a length of the sleeve, so as to correspond to the geometric attributes of the optical elements it contains. The adhesive agent can be an epoxy, or a solder. Both UV and high temperature epoxies are typically employed. The optical elements that are to be coupled can be optical fiber holders (or connectors), GRIN lenses, optical isolators, and optical filters, etc.
A plurality of the fiber-optic couplers described above can be further cascaded, providing a secure and reliable way of interconnecting a variety of optical elements which may require different alignments. Moreover, two or more fiber-optic couplers, in simple or cascaded form, can be telescoped within and bridged by one or more additional sleeves, to further facilitate the interconnections in a fiber-optical network.
The novel features of the present invention will be best understood from the following drawings and detailed description.